Hereinafter, a brief description of carriers will be given.
A user may perform modulation on the amplitude, frequency, and/or phase of a sine wave or a periodic pulse wave to include information which is desired to be transmitted. At this time, the sine wave or pulse wave serving to convey information is referred to as a carrier.
Methods for modulating a carrier include a single-carrier modulation (SCM) scheme and a multi-carrier modulation (MCM) scheme. The SCM scheme performs modulation such that all information is carried on a single carrier.
The MCM scheme divides an entire bandwidth channel of one carrier into subchannels having multiple narrow bandwidths and transmits multiple narrowband subcarriers through respective subchannels.
When the MCM scheme is used, each subchannel may approximate to a flat channel due to a narrow bandwidth. A user may compensate for distortion of a channel using a simple equalizer. Also, the MCM scheme may be implemented at a high speed using Fast Fourier Transform (FFT). Namely, the MCM scheme is favorable during high-rate data transmission as compared to the SCM scheme.
As the capabilities of a base station and/or a terminal have been developed, a frequency bandwidth which can be provided or used by the base station and/or the terminal has been enlarged. Accordingly, in the embodiments of the present invention, a multi-carrier system that supports broadband by aggregating one or more carriers is disclosed.
In other words, the multi-carrier system, which will be described hereinafter, uses carriers by aggregating one or more carriers, unlike the afore-mentioned MCM scheme which uses carriers by segregating one carrier.
In order to efficiently use multiple bands (multi-bands or multi-carriers), a technique in which one medium access control (MAC) entity manages multiple carriers (for example, multiple frequency carriers) has been suggested.
FIG. 1(a) and FIG. 1(b) illustrate methods for transmitting and receiving signals based on a multi-band radio frequency (RF) scheme.
In FIG. 1, one MAC layer in each of a transmitting end and a receiving end may manage multiple carriers to efficiently use the multiple carriers. At this time, to effectively transmit and receive the multiple carriers, it is assumed that both the transmitting end and the receiving end may transmit and receive the multiple carriers. Since frequency carriers managed by one MAC layer do not need to be contiguous, the above method enables flexible resource management. More specifically, the frequency carriers may have contiguous aggregation or non-contiguous aggregation.
In FIG. 1(a) and FIG. 1(b), physical layers (PHY 0, PHY 1, . . . , PHY n−2, and PHY n−1) represent multiple bands, each of which may have a frequency carrier (FC) size allocated for a specific service in accordance with a frequency policy which is previously defined. For example, PHY 0 (RF carrier 0) may have a frequency band size allocated for a general FM radio broadcast, and PHY 1 (RF carrier 1) may have a frequency band size allocated for cellular phone communication.
Although each frequency band may have a different FA size depending on their characteristics, it is assumed in the following description that each frequency carrier (FC) has a size of A MHz for convenience of description. Each frequency allocation (FA) band may be represented by a carrier frequency that enables a baseband signal to be used in each frequency band. Thus, in the following description, each frequency allocation band will be referred to as a “carrier frequency band” or will simply be referred to as a “carrier” representing each carrier frequency band unless such use causes confusion. Also, in the recent 3rd generation partnership project (3GPP) long term evolution-advanced (LTE-A), the carrier may also be referred to as a “component carrier” to discriminate it from a subcarrier used in the multi-carrier system.
As such, the “multi-band” scheme may also be referred to as a “multi-carrier” scheme or a “carrier aggregation” scheme.
FIG. 2 is a diagram illustrating an example of the use of multiple carriers in a general wireless communication system.
The multiple carriers of the general technology may employ contiguous carrier aggregation as shown in FIG. 2(a) or non-contiguous carrier aggregation as shown in FIG. 2(b). The combination unit of such carriers is a basic bandwidth unit of a general legacy system (e.g., Long Term Evolution (LTE) in an LTE-advanced system or IEEE 802.16e in an IEEE 802.16 m system). In a multi-carrier environment of the general technology, two types of carriers are defined as follows.
First of all, a first carrier (also, referred to as a primary carrier) is the carrier used by a mobile station and a base station to exchange traffic and full PHY/MAC control information. Further, the primary carrier may be used for general operations of the mobile station, such as network entry. Each mobile station has only one primary carrier per cell.
A second carrier (also, referred to as a secondary carrier) is an additional carrier that may be used for exchange of traffic based on base station specific allocation commands and rules, typically received from the first carrier. The secondary carrier may also include control signaling for supporting multi-carrier operation.
In the general technology, the carriers of a multi-carrier system based on the above-described primary and secondary carriers may be classified into a fully configured carrier and a partially configured carrier as follows.
First of all, the fully configured carrier refers to a carrier for which all control signaling actions including synchronization, broadcast, multicast and unicast control channels are configured. Further, information and parameters regarding multi-carrier operation and the other carriers may also be included in the control channels.
The partially configured carrier refers to a carrier in which all control channels for supporting downlink (DL) transmission are configured in a downlink carrier other than a pair of uplink carriers during Time Division Duplex (TDD) DL transmission or in a Frequency Division Duplex (FDD) mode.
Generally, the mobile station may perform initial network entry through the primary carrier, and may exchange mutual multi-carrier capability information with the base station in a registration process for exchanging an Advanced Air Interface (AAI) registration request response (AAI_REG-REQ/RSP) message.
Therefore, the mobile station acquires information of available carrier(s) of the base station, and the base station may allocate at least one of available secondary carriers to the mobile station. Prior to performing data exchange through the allocated carrier, the mobile station should perform activation for the corresponding carrier. In this respect, the present invention suggests a method for more efficiently activating a secondary carrier and an apparatus for performing the method.